File:Cardinal gems.png|thumb|250px|Group of precious and semiprecious stones —both uncut and faceted— including (''clockwise from top left'') diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster.
A '''gemstone''' (also called a '''gem''', '''fine gem''', '''jewel''', '''precious stone''' or '''semi-precious stone''') is a piece of mineral crystal
which, in cut and polished form, is used to make jewellery|jewelry
or other adornments.
[[http://www.askoxford.com The Oxford Dictionary Online] and [http://mw1.merriam-webster.com/dictionary/gemstone Webster Online Dictionary]]
However, certain Rock (geology)|rock
s (such as lapis lazuli
) or organic chemistry|organic
materials that are not minerals (such as amber
, jet (lignite)|jet
, and pearl
) are also used for jewelry and are therefore often considered to be gemstones as well....